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1. Single-shot visualization of the optical Kerr effect, ionization, and rotational Raman effect during laser matter interactions via frequency-domain holography

   Dempsey, Dennis ; Nagar, Garima ; Agnes, Jack ; Berger, Russell ; Shim, Bonggu ( June 2021 , APS Division of Atomic, Molecular and Optical Physics Meeting 2021)

   We visualize the ultrafast dynamics caused by intense femtosecond laser pulses in both thin flexible glass as well as gaseous atoms and molecules using single-shot Frequency Domain Holography (FDH) [1-3]. FDH is a robust, single-shot, time-resolved visualization technique that employs chirped pulses. Femtosecond laser micromachining of glass materials relies critically on the Kerr effect and ionization, thus direct observation of their dynamics can help produce optical devices such as waveguides. For gases, single-shot visualization of laser-matter interactions will allow for a better understanding of nonlinear optical phenomena such as filamentation [4] and Raman-induced extreme spectral broadening [5]. Using FDH, we have previously observed the ionization dynamics of thin, flexible glass and measured its nonlinear index [3], and are currently investigating the ultrafast dynamics of gases under intense laser fields. [1] S. P. Le Blanc et al., Opt. Lett. 56, 764-766 (2000). [2] K. Y. Kim et al., APL, 88 4124-4126 (2002). [3] S. Huang et. al., OFC 1-3 (2014). [4] A. Couairon et al., Phys. Rep. 441, 47 (2007). [5] D. Dempsey et al. Opt. Lett. 45, 1252-1255 (2020). 

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2. Fabrication of waveguides in flexible glass via femtosecond laser micromachining and visualization of ultrafast dynamics of the laser-glass interaction

   Agnes, J ; Nagar, G ; Dempsey, D ; Batista, N ; Sutherland, J ; Shim, B ( November 2021 , 63rd Annual Meeting of the APS Division of Plasma Physics)

   We fabricate waveguides in Corning® flexible glass using Femtosecond Laser Micromachining (FLM) and visualize the ultrafast plasma dynamics which lead to waveguide formation via time-resolved interferometry. Due to minimal thermal effects and highly-nonlinear optical processes [1], FLM is an ideal tool to fabricate waveguides in glass with high precision and without post processing. We optimize laser fabrication of waveguides by varying scanning speed and pulse energy and, in particular, achieve waveguides with circular cross-sections using slit beam shaping [2]. Further optimization requires investigation of the underlying dynamics of how structural changes in glass are made during and after laser-glass interactions. Thus, we visualize the creation and recombination of plasma in glass which leads to the formation of waveguides using time- resolved interferometry [3]. [1] Rafael R. Gattass and Eric Mazur, Nature Photonics 2, 219–225 (2008)); [2] M. Ams et al. Opt. Express 13, 5676-5681 (2005); [3] G. C. Nagar, D. Dempsey, and B. Shim, Communications Physics 4, 96 (2021). 

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3. Ultrafast observation of intense light-matter interactions in flexible glass via single-shot frequency domain holography

   https://doi.org/10.1364/FIO.2020.FM1C.4  

   Dempsey, Dennis ; Nagar, Garima C. ; Renskers, Christopher K. ; Grynko, Rostislav I. ; Sutherland, James S. ; Shim, Bonggu ( September 2020 , Frontiers in Optics / Laser Science)

   We use frequency domain holography (FDH) to spatio-temporally visualize the laser-matter interaction caused by the optical Kerr effect and plasma in flexible Corning® Willow® Glass in a single-shot. 

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4. Single-shot ultrafast visualization and measurement of laser–matter interactions in flexible glass using frequency domain holography

   https://doi.org/10.1364/OL.382645  

   Dempsey, Dennis ; Nagar, Garima C. ; Renskers, Christopher K. ; Grynko, Rostislav I. ; Sutherland, James S. ; Shim, Bonggu ( February 2020 , Optics Letters)

   We perform single-shot frequency domain holography to measure the ultrafast spatio-temporal phase change induced by the optical Kerr effect and plasma in flexible Corning Willow Glass during femtosecond laser–matter interactions. We measure the nonlinear index of refraction ($n_2$) to be$(3.6\pm <\#comment/>0.1)\times <\#comment/>{10}^{-<\#comment/>16}{\mathrm{c}\mathrm{m}}^2/\mathrm{W}$and visualize the plasma formation and recombination on femtosecond time scales in a single shot. To compare with the experiment, we carry out numerical simulations by solving the nonlinear envelope equation.

    

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5. Single-shot spatio-temporal visualization of plasma and optical nonlinearity via single-shot frequency-domain holography

   Dempsey, D. ; Nagar, G. ; Agnes, J. ; Berger, R. ; Shim, B. ( November 2021 , 63rd Annual Meeting of the APS Division of Plasma Physics)

   We observe the ultrafast dynamics of solids and gases under intense femtosecond light in a single shot using Frequency Domain Holography (FDH) [1-3]. FDH is a time-resolved visualization technique that utilizes a pump pulse and two chirped laser pulses (reference and probe) for ultrafast phase measurements. Single-shot visualization of laser-matter interactions will allow for increased understanding of nonlinear optical phenomena such as Raman-induced extreme spectral broadening [4], filamentation [5], and plasma generation and recombination [3]. [1] S. P. Le Blanc et al., Opt. Lett. 56, 764-766 (2000). [2] K. Y. Kim et al., APL, 88 4124-4126 (2002). [3] D. Dempsey et al. Opt. Lett. 45, 1252-1255 (2020) [4] J. Beetar et al., Science Advances 6, eabb5375 (2020) [5] A. Couairon et al., Phys. Rep. 441, 47 (2007). 

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